of a population density of tens of thousands of people per square mile. now, the only reason why that was possible, especially in a nonindustrial context, was that you had a very effective agricultural environment around fez within, say, 15 or 20 miles radius. but you also had very effective forms of nonhuman transport -- donkeys, camels, horses, mules -- that could bring in all of the kinds of supplies that the city needed. now, that's one reason why you had such high population densities. one of the effects of really high population densities, of course, is to create very dense urban markets, lots of consumers concentrated in small spaces. and this is one of the reasons why fez has such a high degree of urban specialization. keach: as in ancient ostia, almost everyone in fez is a full-time specialist.